1. Field of the Invention
The present invention relates to immunoassays, and, more particularly, to the use of immunoassays to detect contaminants in foodstuffs. Still more particularly, the present invention provides an antibody detection system for detecting contaminants in packaged foodstuffs. The present invention has applications in toxicology, agriculture, and food safety.
2. The Related Art
The mass production and distribution of food, especially meat, poultry, and fish products, has contributed greatly to the good health enjoyed by most modern societies. In particular, the rise of industrial-scale meat, poultry, and fish processing and distribution allows even those living in very remote locations the opportunity to enjoy the nutritional and gastronomic benefits of a balanced diet. As a result, many childhood diseases associated with poor nutrition have all but disappeared from modern societies.
However, the mass production and distribution of food, and, more particularly, meat, has raised concerns. Changes in production and inspection of meat, poultry, fish processing and dining habits (modern societies tend to dine out more frequently) have lead to an increase in food contamination. The increase in the distribution and consumption of tainted food has been implicated in several outbreaks of food poisoning in recent years that have lead to numerous illnesses and deaths. Of particular concern has been the measured increase in meat contaminated with E. coli bacteria, especially the strain denoted 0157:H7. E. coli O157:H7 produces a toxin that attacks the gastrointestinal tract causing severe cramping, abdominal pain, watery or bloody diarrhea, vomiting, and/or fever (Brody 1998). In some cases, the toxin can even cause kidney failure, which is fatal in about 30 percent of cases. Recently, the increase in E. coli-tainted meat has been attributed to the practice of raising cattle on high-grain diets that are known to provide more desirable meats (Diez-Gonzalez, Callaway et al. 1998).
In addition, other food-born toxins exist. Salmonella has been found increasingly in chicken and raw eggs. Listeria has been found in dairy products that have been improperly pasteurized. Ciguatoxins can be found in fish. These toxins are especially dangerous as they generally are not affected by cooking. Shell fish, such as oysters, mussels, and clams, often are contaminated with bacteria from waste water that is dumped in either untreated or partially treated form into coastal waters from which the shell fish are harvested. In addition, the increasing popularity of raw fish has also lead to increased incidents of food poisoning from contaminated fish. Moreover, recent outbreaks of xe2x80x9cmad cow diseasexe2x80x9d have lead health officials to worry about the transmission of prion-based diseases from animals to man by the consumption of contaminated meat and/or meat products.
Often, the presence of dangerous bacteria is difficult for the consumer to detect. First, the amount of bacteria necessary to cause infection can be too small for detection by sight or smell. Second, the presence of contamination cannot be easily detected in packaging that blocks smells and hides most food surfaces. Thus, there is a need to provide consumers and distributors with an efficient, accurate means for detecting the presence of contaminants in foodxe2x80x94especially packaged food. Ideally, such means for detecting food contaminants would be observable by the consumer or at the point of sale and inexpensive to provide.
One attempt to provide such a solution is described in U.S. Pat. No. 5,306,466 to Goldsmith and in U.S. Pat. No. 5,869,341 to Woodaman. These patents describe a bar code formed by depositing a known toxin in a xe2x80x9cbar codexe2x80x9d pattern on a substrate and ligating to the bound toxin a color-labeled anti-toxin to provide a visible bar code. The labeled toxinxe2x80x94anti-toxin substrate is located in a well set into the food container that collects juices and other moisture from the packaged food. Toxins in the juices compete with the bound toxin for the labeled anti-toxin. As more of the anti-toxin binds to the solution-borne toxin, the bar code is eroded leading to a detectable change in the labelxe2x80x94either visually or by using a bar code reader which returns a xe2x80x9cnullxe2x80x9d or xe2x80x9cerrorxe2x80x9d result upon scanning the eroded bar code. Unfortunately, such assays are complex and expensive to produce. Thus, the bar code described in the ""466 and ""3411 patents is not especially attractive for mass production of food packaging. Moreover, the bar code described in the ""466 and ""3411 patents cannot readily provide the identity of the toxin (or toxins) detected to a database when the bar code is scanned.
Thus, there remains a need for a highly scalable, accurate food contamination assay that can be readily perceived at various check points in the distribution chain and at the point of sale.
The present invention provides a food contamination assay that is accurate, easy to produce, and scalable. Thus, the present invention will be seen to provide a food contamination assay that can be mass produced for modern food packaging and distribution networks to provide produces, shippers, and consumers warning of food contamination.
In a first aspect, the present invention provides a toxin contamination detector. In one embodiment, the contamination detector of the invention includes a substrate on which a bar code is printed. The bar code has a first color (e.g., black) that is effective to reflect light from a bar code scanning device to produce a bar code result. A toxin indicator is also included. The toxin indicator has a second color in the absence of toxin, which second color does not substantially affect or alter the bar code result. However, the toxin indicator presents a third color in the presence of toxin which substantially changes the bar code result; thereby indicating the presence of toxin.
In one embodiment, the toxin indicator is deposited over the bar code so as to provide a background color against which the bar code is scanned or otherwise read. In another embodiment, the third color presented by the toxin indicator in the presence of toxin is effective to cause a xe2x80x9cnullxe2x80x9d bar code result when the bar code is scanned. In a more particular embodiment, the toxin indicator comprises a polydiacetylene (xe2x80x9cPDAxe2x80x9d) polymer coupled with a toxin-recognizing moiety. Still more specifically, the toxin indicator comprises a PDA-containing vesicle.
In another embodiment, the substrate is substantially transparent and the toxin indicator is deposited behind the substrate. In a still more particular embodiment, the toxin indicator is deposited to provide a second bar code result that is different from the first bar code result when the toxin indicator is exposed to toxin. In yet a more particular embodiment, the second bar code is effective to identify the toxin. The toxin indicator can be a PDA polymer or PDA-containing vesicle.
In as second aspect, the present invention provides a method for identifying toxin contamination in which a substrate having a first bar code printed thereon to produce a first bar code result is provided. A toxin indicator is provided proximate to the first bar code. The toxin indicator has a second color in the absence of toxin, which second color does not substantially affect or alter the bar code result. However, the toxin indicator presents a third color in the presence of toxin which substantially changes the bar code result; thereby indicating the presence of toxin. The toxin indicator is exposed to the toxin to change color from the second color to the third color. The bar code is then scanned to detect the presence of the toxin. Alternatively, the toxin indicator can be deposited to provide a second bar code.
In one embodiment, the result of the scan is stored in a database. In another embodiment, the toxin indicator is coupled with the first bar code to provide a xe2x80x9cnullxe2x80x9d or xe2x80x9cerrorxe2x80x9d result when the bar code is scanned. In still another embodiment, the toxin indicator provides a background color for the first bar code.
These and other aspects and advantages will become apparent when the Description below is read in conjunction with the accompanying Drawings.